Electric power semiconductor devices have been widely spreading in all products such as industrial apparatuses, consumer electrical appliances, and information terminals; in particular, downsizing and high-reliability are required in consumer electrical appliances. Moreover, because an electric power semiconductor device deals with a high voltage and a large current, a great deal of heat is generated; thus, it is required to efficiently radiate the heat to the outside. Furthermore, it is also required that a wide bandgap semiconductor material such as SiC, which may be mainly utilized in the years to come because of a high operating temperature and a high efficiency thereof, can be applied to an electric power semiconductor device.
In general, in a small electric power semiconductor device, an electric power semiconductor element is often disposed on a substrate on which an electric circuit is formed; when heat generated in the electric power semiconductor element is radiated to the outside through the substrate, the heat conductivity of the substrate itself provides a large effect to the heat radiation performance. However, an AlN substrate, which allegedly has superior heat conductivity, is difficult to obtain. In contrast, an alumina substrate or a glass-epoxy substrate, which is easily obtained, has heat conductivity of only one-twentieth to one-thousandth of the heat conductivity of high-heat-conductivity metal such as copper; therefore, high heat radiation performance cannot be expected.
Accordingly, it is conceivable that in order to secure the heat radiation performance, the rear side of an electric power semiconductor element is directly connected with a heat radiation material through a high-heat-conductivity insulating layer. In that case, it is conceivable that wiring of the front side thereof is implemented by soldering the front side with an interposer substrate (e.g., refer to Patent Document 1). However, the electrode on the surface of a common electric power semiconductor element formed under the assumption of wire bonding is not suitable for soldering; therefore, soldering requires special machining. Thus, it is conceivable that an electric power semiconductor element is inserted into the opening of an interposer substrate and a technology (e.g., refer to Patent Document 2 or 3) in which wiring of a common electric power semiconductor element can be implemented through wire bonding is utilized.